Ablation catheter

ABSTRACT

An ablation catheter  10  includes an elongate carrier  12.  A first loop  14.1  is arranged at, or adjacent, a distal end of the carrier  12.  At least one sensing electrode  40  is carried on the first loop  14.1  for sensing irregular electrical activity in a patient&#39;s body. At least one further loop  14.2  is arranged proximally relative to the first loop  14.1  on the carrier  12  in a fixed orientation relative to the first loop  14.1.  At least one ablating electrode  42  is carried on the second loop  14.2  for ablating a site of the patient&#39;s body where irregular electrical activity occurs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/514,308,filed Nov. 12, 2004, which is a national phase filing of PCT/AU03/00559,filed May 9, 2003, which claims the benefit of Australian applicationPS2264, filed May 13, 2002, the disclosures of which are incorporatedherein by reference in their entirety.

FIELD

This invention relates to a catheter. The invention relatesparticularly, but not necessarily exclusively, to an ablation catheterfor the treatment of atrial fibrillation.

BACKGROUND

Atrial fibrillation is a condition that affects large groups of peoplewith new patients being diagnosed each year. These patients have a lowerquality of life as well as having up to a seven times increase in thelikelihood of heart attacks or strokes. Current therapies include drugtreatment or defibrillation, both palliative forms of treatment. Overthe past few years, a number of research groups have been investigatingcurative treatment involving ablative techniques using radio frequency(RF), ultrasound, laser or microwave energy or cryoablation techniques.

Ablation therapy, while being promising, requires complex catheterdesigns. Such catheters also have to be reasonably thin to be manoeuvredthrough a patient's vascular system.

A current approach is the use of a catheter in the shape of a lassowhich has a number of electrodes used for diagnostic purposes only. Thelasso is positioned through the left atrium of the heart in pulmonaryveins. As the lasso is round in shape, it surrounds the inside of thevein. Different sizes of catheters are required depending on the sizeand shape of the ostium. A typical procedure uses a first catheter tosense regions of irregular electrical activity and a second, separate,ablation catheter to ablate the specific site of irregular electricalactivity. The procedure is repeated at various sites until all sites ofirregular electrical activity have been blocked. One of thedisadvantages associated with this procedure is the difficulty inguiding the ablation catheter to the exact site of the vein at whichablation is to occur. In this regard, it must be borne in mind that thefirst catheter which is used to sense the irregular electrical activityneeds to be retained in position while the second catheter is insertedthrough the patient's vascular system to the site to guide the ablationcatheter to that site. In addition, too much energy can lead toexcessive tissue damage which can lead to stenosis of the blood vessel.Conversely, too little energy or insufficient ablated sites can lead toa re-occurrence of the irregular, electrically conductive pathways andtherefore the likelihood of further atrial arrhythmia.

SUMMARY

According to a first aspect of the invention, there is provided anablation catheter which includes:

an elongate carrier;

a first loop arranged at, or adjacent, a distal end of the carrier;

at least one sensing electrode carried on the first loop for sensingirregular electrical activity in a patient's body;

at least one further loop arranged proximally relative to the first loopon the carrier in a fixed orientation relative to the first loop; and

at least one ablating electrode carried on the second loop for ablatinga site of the patient's body where irregular electrical activity occurs.

Preferably, the catheter includes a plurality of sensing electrodesarranged at circumferentially spaced intervals about the first loop anda plurality of ablating electrodes arranged at circumferentially spacedintervals about the second loop. When viewed longitudinally along thecarrier, each ablating electrode of the second loop may be aligned witha sensing electrode of the first loop.

The elongate carrier may include a tubular member defining a lumen and ashape forming member carried in the lumen for forming the loops. Theshape forming member may be of a shape memory alloy such as a nickel,titanium alloy.

The tubular member may act as a mandrel for electrical conductors forthe electrodes of the first loop and the second loop, the conductorsbeing arranged about an outer surface of the tubular member and beingcovered with a coating of an insulating material. This leaves a lumen ofthe tubular member free for the passage of other elements, such assteering cables, conduits for cooling fluids etc. At predeterminedlocations along the coating, the coating may be removed to expose theconductors and electrodes may be applied at these exposed locations.

The tubular member may be folded back on itself to form a distal hairpinand a pair of limbs extending from the hairpin, the limbs having a pairof proximal ends, the loops being carried on the limbs and a size ofeach loop being adjustable by appropriate manipulation of the proximalend of at least one of the limbs.

An electrically isolating discontinuity may be arranged between theloops isolating the conductors of the first loop from the conductors ofthe second loop. The second loop may be arranged on one of the limbsproximally of the discontinuity with the first loop also being arrangedon the first limb but between the discontinuity and the hairpin, theelectrical conductors for the ablating electrodes of the second loopextending along the one limb and the electrical conductors for thesensing electrodes of the first loop extending along the other limb andthrough the hairpin into the one limb.

It will be appreciated that, because the lumen is free of conductors, itcan be made more narrow. Also, the fact that conductors for each of theloops run in separate limbs of the tubular member means that moreelectrodes can be carried on each loop without adversely affecting thesize of the catheter. As a result, the accuracy of sensing measurementsand ablating procedures is improved because greater resolution ispossible than has heretofore been the case.

In the manufacture of the catheter, the conductors may be mounted on thetubular member prior to folding the tubular member. The electrodes maybe formed at the desired locations along the length of the conductorswhere after the tubular member is folded back on itself and cut toisolate the electrodes on one loop from the electrodes on the other loopwith each set of electrodes having its own conductors. The shape formingmember may then be inserted into the lumen of the tubular member to formthe loops.

The first loop, which is arranged at a distal end of the catheter mayhave only electrodes without any temperature sensing means and may beused for sensing electrical activity in the pulmonary vein. The secondloop, being proximally arranged relative to the first loop may, in use,be located at, or adjacent, the ostium of the pulmonary vein and may beused for ablating purposes. Thus, the second loop may include theelectrodes and the temperature sensing means. It will be appreciatedthat the catheter may comprise more than two loops, with one being usedfor sensing and two being used for ablation or vice versa.

The electrodes of the second loop of the catheter may be used both forsensing undesirable or irregular electrical activity at, or adjacent,the ostium of the pulmonary vein and for ablating tissue at, oradjacent, the ostium of the pulmonary vein at where such undesirableelectrical activity occurs. Thus, where any electrode of the first loopor the second loop senses undesirable electrical activity, the relevantelectrode or electrodes of the second loop may be used to ablate thetissue to form a lesion in the region of the ostium to disrupt theelectrically conductive pathway in the tissue to reduce atrialfibrillation.

The catheter may include a tubular introducer for introducing thecarrier into the patient's body, the carrier being slideably received ina passage of the introducer and being slideable relative to theintroducer between a first, retracted position in which the loops arecontained in a collapsed configuration in the passage of the introducerand a second, extended configuration in which the loops are in anexpanded, loop-shaped configuration and are distally arranged relativeto a distal end of the introducer. When the loops are in their second,extended configuration, each loop may lie in a plane transverse to alongitudinally axis of the carrier. The planes may be substantiallyparallel to each other.

As a result of the looped arrangement of the electrodes, when thecatheter is inserted into the blood vessel, an operator will know whichparts of each loop and, hence, which side of each electrode is incontact with a wall of the blood vessel and which side is in contactwith blood within the blood vessel. As it is undesirable to impart heatto the blood carried in the blood vessel, each electrode may becuff-shaped to extend only partway about the periphery of the carrier,the arrangement being such that the electrodes are arranged on an outerside of their loops. By “cuff-shaped”, it is meant that the electrodesare semi-circular cylindrical in shape.

Each of at least certain of the electrodes at least on the second loopmay have a temperature measuring facility associated with it. Thetemperature measuring facility may be a thermocouple. Those electrodesoperative also to measure temperature may therefore have threeconductors associated with them. Those electrodes used only for sensingor ablating may only have a single conductor associated with them.

According to a second aspect of the invention, there is provided anablation catheter which includes

an elongate carrier having a loop defined at a distal end, the loopcomprising a first arm and a second arm, the arms of the loop being atleast partly electrically isolated with respect to each other; and

at least one electrode arranged on each arm of the loop.

Preferably, each arm carries a plurality of electrodes. The electrodesmay be serially arranged along a length of each arm.

The carrier may comprise a tubular member defining a lumen with a shapeforming member being received in the lumen for forming the loop.

The tubular member may act as a mandrel for electrical conductors forthe at least one electrode of the loop, the conductors being arrangedabout an outer surface of the tubular member and being covered in acoating of an insulating material.

The tubular member may be folded back on itself to form a distal hairpinand a pair of limbs extending from the hairpin, each limb havingproximal end, the arms of the loop being defined by distal portions ofthe limbs on opposite sides of the hairpin.

The arms of the loop may be electrically isolated from each other at adistal end of the loop. Thus, the tubular member may include anelectrically isolating discontinuity at the distal end of the arms, moreparticularly, at the hairpin. For example, the arms may be cut and thenre-connected in an electrically isolated manner.

By “at least partly electrically isolated, it is meant that, in respectof most conductors of each limb, the conductors terminate before, or at,the discontinuity. However, it may be required that at least certain ofthe conductors traverse the discontinuity, ie. extend up through onelimb and return through the other limb. Such conductors would then notbe terminated before, or at, the discontinuity.

A temperature measuring facility may be associated with at least certainof the electrodes.

The electrodes may be shaped only to be on an operatively outer part ofthe loop. More specifically, each electrode is substantiallysemi-cylindrical in shape, or cuff-shaped, as opposed to being in theform of a band or annulus.

The semi-cylindrical electrodes may be longer than band-shapedelectrodes so that a surface area of each semi-cylindrical electrode issubstantially the same as that of a conventional band-shaped, ablatingelectrode to have the same current density in the semi-cylindricalablating electrodes, in use.

According to a third aspect of the invention, there is provided anablation catheter which includes

an elongate carrier defining an outer periphery; and

at least one ablating electrode carried on said outer periphery, said atleast one ablating electrode being arranged only partially about theperiphery of the carrier.

The outer periphery may be a radially outer part of at least one loopcarried by the carrier and the at least one electrode may be carriedpartially about the radially outer part of the at least one loop. The atleast one electrode may be of semi-cylindrical shape.

In the case of all aspects as described above, a source of energy foreffecting ablation may be selected from the group comprising radiofrequency, microwave, ultrasound, laser and cryoablative energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described by way of example with reference to theaccompanying drawings in which:

FIG. 1 shows a schematic representation of an ablation catheter, inaccordance with a first aspect of the invention, in an initial stage offormation;

FIG. 2 shows a schematic representation of the catheter;

FIG. 3 shows a schematic representation of an interior cross section ofthe catheter;

FIG. 4 shows a three dimensional view of an ablation catheter, inaccordance with the first aspect of the invention;

FIG. 5 shows a three dimensional view of an ablation catheter, inaccordance with a second embodiment of the invention; and

FIG. 6 shows a schematic, cross sectional view of an ablation catheter,in accordance with a third aspect of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the drawings, reference numeral 10 generally designates an ablationcatheter, in accordance with an embodiment of the invention. Thecatheter 10 include an elongate carrier in the form of a tubular member12 having a loop 14 defined at a distal end of the carrier 12, the loop14 being formed by two arms 18, 22. The arms 18, 22 are joined at adistal end of the loop 14. A plurality of electrodes 16 is carried onone arm 18 of the loop 14 with a similar number of electrodes 20 beingcarried on the opposed arm 22 of the loop 14.

The tubular member 12 defines a lumen 24.

In the fabrication of the catheter 10, in accordance with one embodimentof the invention and as shown in FIG. 1 of the drawings, the tubularmember 12 is folded back on itself into a substantially hairpin shape todefine a pair of limbs 26, 28 joined at a hairpin 29. Conductors, fiveof which are shown schematically at 30 in FIG. 3 of the drawings, areembedded in a wall of the tubular member 12. In the fabrication of thetubular member 12, once the conductors 30 have been placed in positionabout the outside of a part of the tubular member 12 defining the lumen24, a covering or coating 31 of an insulating material is applied to theconductors 30 to form the finished tubular member 12.

At the distal end of the tubular member 12, the coating of insulatingmaterial 31 is removed to expose the conductors 30. Metal is applied bya deposition technique to form the electrodes 16, 20. The metal of theelectrodes 16, 20 is of a bio-compatible material such as a noble metal,for example, platinum.

Once the electrodes 16, 20 have been formed, the tubular member 12 iscut at its distal end, as indicated at 32 in FIGS. 1 and 2 of thedrawings. This includes cutting the conductors 30. The cut ends arere-joined in an electrically isolated manner to form the two arms 18, 22of the loop 14.

As illustrated in FIG. 3 of the drawings, a further tube 34 is insertedinto the lumen 24 of the tubular member 12. This tube 34 accommodates ashape forming member 36 such as a length of nickel, titanium alloy(Nitinol™) which is used in forming each arm 18, 22 of the loop 14, aswill be described in greater detail below. The length of shape formingmember 36 has two, protruding, proximal ends 36.1

The catheter 10 includes an introducer or sleeve 38 in which the hairpinshaped tubular member 12 is received for use The ends 36.1 of the shapeforming member 36 protrude from a proximal end of the introducer 38 andare used for adjusting the size of the loop 14 to cater for varioussizes of pulmonary vein ostia. The introducer 38 includes a steeringmechanism (not shown) for steering the catheter 10 through the vascularsystem and heart of a patient undergoing treatment.

In use, to treat atrial fibrillation, the catheter 10 is inserted viathe patient's vascular system and the left atrium of the heart into theostium of the pulmonary vein to be treated where atrial arrhythmia maybe occurring. To facilitate insertion of the catheter 10, the loop 14 isretracted into the introducer so that the loop 14 adopts a collapsedconfiguration within the introducer 38 as the introducer 38 is steeredto the relevant site by an operator. At the desired location relative tothe ostium, the tubular member 12 is urged towards the distal end of theintroducer 38 to eject the loop-defining part of the tubular member 12out of the distal end of the introducer 38, the length of shape formingmember 36 acting on the distal end of the tubular member 12, as thedistal end of the tubular member 12 escapes from the introducer 38, toform the arms 18, 22 of the loop 14.

Sensing of electrical activity at or adjacent the ostium takes place bythe electrodes 16 and 20 acting as sensing electrodes.

To assist the clinician in placement of the loop 14 relative to thepulmonary vein, radio opaque tokens (not shown) in the form of bands maybe arranged at various location on the loop 14. The radio opaque bandsmay be identified with certain of the electrodes 16, 20 so that theclinician knows exactly where the electrodes 16, 20 are positioned atthe various locations about the wall of the pulmonary vein. This is onlynecessary if the electrodes 16, 20 are not visible under a fluoroscope.

An additional lumen 44 extends along the lumen 24 of the tubular member12 to the electrodes 16, 20 to provide delivery of a fluid, such as asaline solution, to the electrodes 16, 20 during ablation. Due to thefact that the electrodes 16, 20 are coated on the tubular member 12,this facilitates the formation of an opening through each electrode 16,20 through which the saline solution can be delivered. Instead of thesaline solution being ejected through openings in the electrodes, thesolution could, instead, be circulated through a suitable conduit (notshown) arranged in the lumen 24 of the tubular member 12 and extendingthrough the limbs 26, 28 of the tubular member. In this way, theelectrodes 16, 20 may be cooled allowing for higher energies and deeperlesions while inhibiting overheating of the tissue or blood in thevessel.

FIG. 4 of the drawings shows a configuration where a single loop 14 isprovided. In this embodiment of the invention, the electrodes 16, 20 areused both for sensing of electrical activity as well as for ablatingpurposes.

In the embodiment of the invention shown in FIG. 5 of the drawings, acatheter 10 is provided which includes two loops 14.1 and 14.2. The loop14.1 is arranged at the distal end of the catheter 10 and includes onlysensing electrodes 40 arranged about the loop 14.1.

The loop 14.2 is arranged proximally relative to the loop 14.1 andincludes only ablating electrodes 42 arranged about the loop 14.2.However, if desired, the electrodes 42 of the loop 14.2 are also usedfor sensing of irregular electrical activity, in addition to performingtheir ablating function.

In the formation of the catheter 10 of FIG. 5, the cut 32 formed in thetubular member 12 is arranged proximally of the hairpin 29 so that theloop 14.2 is formed proximally of the cut 32 and the loop 14.1 is formedintermediate the cut 32 and the hairpin 29. The conductors 30 for theloop 142 extend along the limb 26 of the tubular member 12, the limb 26terminating at the cut 32. The conductors 30 for the loop 14.1 extendalong the limb 28 of the tubular member 12, the limb 28 forming thehairpin 29 and terminating at the cut 32. It is to be noted that, inthis embodiment of the invention, it is not essential that theconductors 30 for each of the loops 14.1 and 14.2 extend along separatelimbs. In other words, the cut 32 in the tubular member 12 is notessential.

In use, the catheter 10 of FIG. 5 is used in a similar manner to thatdescribed above with reference to FIG. 4. The catheter 10 is introducedinto the patient's vascular system with the loops 14.1 and 14.2retracted, in a collapsed configuration into the introducer 38. Thecatheter 10 is inserted via the left atrium of the patient's heart. Atthe relevant pulmonary vein, the loops 14.1 and 142 are urged distallyout of the introducer 38 so that the shape forming member 36 causes theloops 14.1 and 14.2 to form. When the loops 14.1 and 14.2 are ejectedfrom the catheter 10, they adopt an erected configuration in which theloops 14.1 and 14.2 lie in planes that are substantially parallel toeach other and transversely to a longitudinal axis of the catheter 10.The loop 14.1 is received within the pulmonary vein with the loop 14.2being arranged at, or adjacent, the ostium. The electrodes 40 and 42 arearranged on the loops 14.1 and 14.2, respectively, so that they arealigned with each other longitudinally along the tubular member 12. Thespacing between the loops 14.1 and 14.2 is such that, in all likelihood,should adverse electrical activity be picked up by one of the electrodes40 of the loop 14.1, the corresponding, aligned electrode 42 of the loop142 can be used to ablate the tissue at the ostium which should resultin ceasing of the adverse electrical activity. Accordingly, this aspectof the invention provides separate electrodes for sensing and forablating purposes.

Referring now to FIG. 6 of the drawings, apart of the catheter 10showing one of the electrodes 16, 20, 40 or 42, in accordance withanother aspect of the invention, is illustrated. The electrodes 16, 20,40 or 42 do not extend all the way about the periphery of the tubularmember 12. Rather, the electrodes 16, 20, 40 or 42 are each in the formof a cuff-like member which extends only part way, approximatelyhalfway, about the periphery of the tubular member 12. Hence, when theloop or loops 14 are formed, the cuff-like electrode 16, 20, 40 or 42 asthe case, are arranged on a part of each loop facing radially outwardlyto be in contact with the wall of the pulmonary vein to effectsensing/ablating. With this configuration of electrodes 16, 20, 40, 42electrical energy is focused towards ablating the tissue rather thanablating and coagulating blood in the vessel. This improves the creationof the lesion in the wall of the vein and optimises the size/depth ofthe lesion while lessening the likelihood of stenosis of the veinoccurring.

A further benefit of this arrangement is that, with comparison to aband-type electrode, the cuff-type electrode 16, 20, 40 or 42 has agreater length to provide a similar surface area to the band-typeelectrode. The greater length of the cuff-shaped electrode 16, 20, 40 or42 means that a longer lesion can be formed with the same currentdensity as presently used.

Further, as illustrated in FIGS. 3 and 6 of the drawings, because theconductors 30 for the electrodes 16, 20, 40, 42 are embedded in a wallof the tubular member 12, it results in a catheter 10 which is thinnerthan multi-electrode catheters of the type presently in use. Thisfacilitates manipulation of the catheter 10 through the vessels and/orheart of the patient. It also means that the lumen 24 of the tubularmember 12 is free to accommodate the length of shape-forming member 36and, where applicable, the conduit 44 for the delivery of a salinesolution.

While the catheter 10 has been described with reference to itsapplication in the treatment of atrial fibrillation, it will beappreciated that the catheter 10 could also be used in otherapplications such as in the treatment of ventricular tachycardia. Itcould also be used in non-cardiac applications such as in the ablationof tumours or of the prostate.

Further, it is to be noted that any electrode that is being used ofablation can have a thermocouple pair underneath it if needed. Thus someof the ablating electrodes have three conductors 30 associated with themwhile others only have one conductor 30. Separate electrodes to be usedas thermocouples could also be provided but this would increase thenumber of electrodes. Such separate electrodes would each have twoconductors 30 associated with them.

An example of a catheter 10 is given below:

A one metre length of 0.4 mm stiff shape forming wire 36 which has twoloops 14.1 and 14.2, each of 20 mm diameter shape formed therein andpositioned halfway along the length of the wire 36 was passed in a lumen24 of a tubular member 12 of 1.6 mm diameter with a Pebax™ jacket 31.The tubular member 12 carried twenty 0.16 mm conductors 30 helicallywound around an outer surface of the lumen 24 and embedded in the jacket31. The tubular member 12 was folded back on itself so that the loops14.1 and 14.2 were arranged at the distal end with the loop 14.2 beingarranged proximally of the loop 14.1. The folded tubular member 12 hadthe ends 36.1 of the shape forming wire 36 protruded from the alignedproximal ends of the tubular member 12 and was inserted in an introducer38 so that the loops 14.1 and 14.2 could be ejected through a distal endof the introducer 38 to adopt their erected configuration. It was shownthat, by manipulating the ends 36.1 of each limb 26, 28 of the tubularmember 12 relative to the introducer 38, the diameter of each of theloops 14.1 and 14.2 could be adjusted independently of each other.

It is a particular advantage of the invention that a catheter 10 isprovided which is used both for sensing and ablating in the treatment ofatrial fibrillation. Also, with the construction of the tubular member12 having the conductors 30 embedded therein, a catheter 10 which is ofthinner construction than catheters of which the applicant is presentlyaware, can be formed resulting in easier manipulation of the catheter10.

Another advantage of the catheter 10 of the present invention is that,in comparison with existing catheters, the split construction of thetubular member 12 means that double the number of conductors 30 can beaccommodated and, consequently, double the number of electrodes 16, 20,40 or 42. This has the benefit that more electrodes can be carried oneach loop 14 without adversely affecting the size of the catheter 10. Asa result, the accuracy of sensing measurements and ablating proceduresis improved because greater resolution is possible than has heretoforebeen the case.

With the double loop configuration of the catheter 10, the fact that theloops 14.1 and 14.2 are in a fixed orientation relative to each otherreduces the risk of the loop 14.1 being inserted too deeply into thepulmonary vein. As a result the likelihood of trauma to the vein isreduced.

Prior art catheters of which the Applicant is aware perform acircumferential ablation. Still another advantage of the presentinvention is that individual electrodes can be controlled independentlyto ablate small, segmented regions of tissue rather than creating anentire circular lesion. As a result, less trauma is caused to thepatient and more accurate directing of the ablating at the target sitecan be effected.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1-27. (canceled)
 28. An ablation catheter which includes an elongatecarrier defining an outer periphery, the elongate carrier comprising atubular member defining a lumen, electrical conductors arranged about apart of the tubular member defining the lumen and the conductors beingcovered with a coating of an insulating material so that the conductorsare embedded in a wall of the tubular member with the coating definingthe outer periphery of the tubular member; and at least one ablatingelectrode carried on the outer periphery, the at least one ablatingelectrode being shaped to be on an operatively outer part only of thecarrier and being in electrical communication with at least some of theconductors of the carrier by removal of a part of the coating ofinsulating material with the at least one electrode overlying theopening.
 29. The catheter of claim 28 in which the outer periphery ofthe carrier is a radially outer part of at least one loop defined by thecarrier and the at least one electrode is carried partially about theradially outer part of the at least one loop.
 30. The catheter of claim28 in which the at least one electrode is of semi-cylindrical shape.